English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Long-term streamflow data within the Chesapeake Bay watershed and surrounding area were analyzed in an attempt to identify trends in streamflow. Data from 30 streamgages near and within the Chesapeake Bay watershed were selected from 1930 through 2010 for analysis. Streamflow data were converted to runoff and trend slopes in percent change per decade were calculated. Trend slopes for three runoff statistics (the 7-day minimum, the mean, and the 1-day maximum) were analyzed annually and seasonally. The slopes also were analyzed both spatially and temporally. The spatial results indicated that trend slopes in the northern half of the watershed were generally greater than those in the southern half. The temporal analysis was done by splitting the 80-year flow record into two subsets; records for 28 streamgages were analyzed for 1930 through 1969 and records for 30 streamgages were analyzed for 1970 through 2010. The mean of the data for all sites for each year were plotted so that the following datasets were analyzed: the 7-day minimum runoff for the north, the 7-day minimum runoff for the south, the mean runoff for the north, the mean runoff for the south, the 1-day maximum runoff for the north, and the 1-day maximum runoff for the south. Results indicated that the period 1930 through 1969 was statistically different from the period 1970 through 2010. For the 7-day minimum runoff and the mean runoff, the latter period had significantly higher streamflow than did the earlier period, although within those two periods no significant linear trends were identified. For the 1-day maximum runoff, no step trend or linear trend could be shown to be statistically significant for the north, although the south showed a mixture of an upward step trend accompanied by linear downtrends within the periods. In no case was a change identified that indicated an increasing rate of change over time, and no general pattern was identified of hydrologic conditions becoming “more extreme” over time. Introduction The U.S. Geological Survey (USGS) has been measuring and recording streamflow throughout the United States (U.S.) since the late 1800s. Long-term records of streamflow are invaluable because of the information that they contain about temporal changes in the discharge of streams and rivers, a major component of the hydrologic cycle. Long-term records are necessary to detect and quantify natural and anthropogenic effects on streamflow. Analysis of long-term streamflow records can reveal information about the response of streamflow to climate and weather, to changes in land use in the watershed, and to changes in withdrawals of stream water for various human uses, because the records integrate those complex and interacting physical processes. Analysis of multiple streamflow records in a region is a particularly powerful tool for determining regional trends that may be related to climate. The topic of climate change and variability is full of uncertainty, and any climatic changes are likely to result in changes to the hydrologic cycle at various scales. Some potential consequences of climate change and variability are changes in water availability for municipal and industrial use, changes in water demand for irrigation, changes in water quality, increased threats to stormwater and wastewater infrastructure, and a global rise in sea level. The longer the period of record of streamflow that is available, the better able hydrologists are to determine trends in streamflow, because shorter records can be dominated by the “noise” of natural variability, as well as long-term persistence (see, for example, Cohn and Lins, 2005). Evaluation of the trends that have taken place up to the present is important for the following reasons: (1) attaining an understanding of natural variability and the persistence of changing hydrologic conditions; (2) developing accurate representations of streamflow that can be useful in design and planning models for water quality, water supply, flood hazard mitigation, and ecosystem protection; and (3) forming a body of knowledge that can be used in the evaluation of models that are designed to forecast future changes in streamflow. Spatial and Temporal Trends in Runoff at Long-Term Streamgages within and near the Chesapeake Bay Watershed By Karen C. Rice and Robert M. Hirsch 2 Spatial and Temporal Trends in Runoff at Long-Term Streamgages within and near the Chesapeake Bay Watershed Eutrophication of coastal water bodies is a problem, both nationally (Bricker and others, 1999) and globally (Bricker and others, 2007). The water quality of Chesapeake Bay is threatened by excess nutrients (in particular, nitrogen and phosphorus) and sediments transported to the bay by runoff from the contributing watershed area. The amount and timing of streamflow to the bay are integral determinants of the amount of nutrients, sediments, and other dissolved constituents that are delivered to the bay. How, when, and where streamflow, and resulting water quality, might change in the future is of great interest to a wide variety of stakeholders. Understanding past and future changes in water quality is important but must be based on an understanding of past and future changes in streamflow. A report by Karl and Knight (1998) documents an increase in precipitation across the U.S. during the 20th century, with winter precipitation only slightly increased but with more pronounced increases in the other seasons, in particular spring and fall. The report defines the six New England States, as well as New York, Pennsylvania, and Maryland, as being part of the Northeastern U.S.; Virginia is included as part of the Southeastern U.S. Karl and Knight (1998) document that precipitation has increased more in the Northeast than in the Southeast. Increased streamflow trends have been reported for the U.S. (Lins and Slack, 1999; McCabe and Wolock, 2002) and the New England States (Collins, 2009). Najjar and others (2009) report a summary of modeling studies that shows projections of streamflow in the Susquehanna River Basin and Mid-Atlantic area for the last quarter of the 21st century. These projections of annual streamflow change range from –25 to 33 percent (Najjar and others 2009). Another study for the Northeastern U.S. indicates that modeled streamflow will become more variable throughout the 21st century (Hayhoe and others, 2007). Finally, a state of the science review for Chesapeake Bay summarizes the wide range of projections for streamflow for the Chesapeake Bay watershed (Pyke and Najjar, 2008). On the basis of the uncertainties concerning projected streamflow in the region, a study of existing streamflow trends in the Chesapeake Bay watershed is needed. The purposes of this study, conducted by the U.S. Geological Survey Environments Program and Hydrologic Network and Analysis Program in cooperation with the Virginia Department of Environmental Quality, were to: (1) compute and analyze long-term (80-year) trends in streamflow in 30 nontidal watersheds within and near the Chesapeake Bay watershed, (2) identify any spatial patterns in the trends, and (3) further explore major variations in the temporal trends over the 80-year record (1930–2010). The scope of this report is to present the results of the spatial and temporal analyses. Although this report does not address future changes to streamflow, the results should serve as a baseline that can be used to compare with hindcasts made by climate models to evaluate the capability of these models to accurately simulate the hydrologic changes that have taken place in the watershed over the last 80 years. Study Area The watershed that encompasses all streams that drain to Chesapeake Bay consists of 165,759 square kilometers (km2) and extends from New York to Virginia. The Chesapeake Bay watershed includes parts of New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia, as well as Washington, D.C. (fig. 1). Parts of the physiographic provinces that lie within the bay watershed are the Appalachian Plateaus, the Valley and Ridge, the Blue Ridge, the Piedmont, and the Coastal Plain (Fenneman and Johnson, 1946). The major river basins that lie within the Chesapeake Bay watershed are the Susquehanna River, Western Shore, Patuxent River, Potomac River, Rappahannock River, York River, James River, and Eastern Shore (Phillips, 2007). Data were analyzed from USGS streamgages located within and near the Chesapeake Bay watershed and having the longest continuous period of daily mean discharge record in common. A total of 23 nontidal streamgages within, and 7 nontidal streamgages near, the Chesapeake Bay watershed were chosen for analysis (fig. 2). This subset of streamgages in the bay watershed was selected because most of the streamgages have continuous daily mean discharge data extending for at least 80 years. The 30 streamgages selected for this analysis have watersheds that range in area from 303 to 62,419 km2 (table 1). The Susquehanna River and its tributaries drain nearly half of the Chesapeake Bay watershed; slightly more than half of the streamgages analyzed in this report are located in the Susquehanna River Basin (table 1). Within the dataset are several streamgages that lie upstream from other streamgages used in the analysis. Thus, a degree of redundancy is present in some of the results, but the difference in drainage area between upstream and downstream sites warrants the inclusion of both. Unfortunately, streamgages located in the Coastal Plain part of the bay watershed, including the Eastern Shore, have records of insufficient length to be included in this analysis. Methods Data were analyzed by comparing the numerical results of calculated flow statistics for the period of record, 1930–2010, and by analyzing two subsets of the period of record, 1930–1969 and 1970–2010. Three annual streamflow statistics were analyzed in this report. They are measures of high flow, averag

Spatial and temporal trends in runoff at long-term streamgages within and near the Chesapeake Bay Watershed